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United States Patent |
5,249,935
|
Burgdorf
|
October 5, 1993
|
Piston pump
Abstract
A piston pump is described which adapts the output flow to the supply flow
which is intended in particular for use in a hydraulic brake slip control
apparatus, the pump having a pump housing (2) with working chambers (9,
10) which are connectible to supply lines via an inlet valve (5) and an
outlet valve (6). Working pistons (15) defining in part the working
chambers are cyclically movable to increase and decrease the volume of the
working chambers (9, 10) and are guided in cylinder bores (11, 12) and
driven by a an eccentric (14) in order to perform stroke movements. The
cylinder bores (11, 12) also receive charging pistons (18) which also
define in part the working chambers (9, 10) and which are movable to
decrease the volume of the working chambers (9, 10) by way of compression
springs (20) supported on the pump housing (2) and which, via a pin (21),
can be pressed against the working pistons (15). The charging pistons (18)
are limited in their movement out of the working chambers (9, 10) by stops
on the pump housing (2). The charging pistons (18) are moved inwardly,
overcoming the frictional grip of a seal (22) to reduce the working
chamber volume and thus the flow rate of the piston pump in order to avoid
cavitation, in the event that the quantity of pressure fluid delivered via
the inlet valves (5) does not suffice to preserve a predetermined suction
pressure in the working chambers (9, 10).
Inventors:
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Burgdorf; Jochen (Offenbach-Rumpenheim, DE)
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Assignee:
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Alfred Teves GmbH (Frankfurt am Main, DE)
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Appl. No.:
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855637 |
Filed:
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May 4, 1992 |
PCT Filed:
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July 9, 1991
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PCT NO:
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PCT/EP91/01277
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371 Date:
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May 4, 1992
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102(e) Date:
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May 4, 1992
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PCT PUB.NO.:
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WO92/04216 |
PCT PUB. Date:
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March 19, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
417/415; 92/60 |
Intern'l Class: |
F04B 021/00 |
Field of Search: |
417/415
92/60
|
References Cited
U.S. Patent Documents
3168045 | Feb., 1965 | Sebastiani | 92/60.
|
Primary Examiner: Bertsch; Richard A.
Assistant Examiner: Scheuermann; David W.
Attorney, Agent or Firm: Seitter; Robert P., Lewis; J. Gordon
Claims
I claim:
1. A piston pump comprising a pump housing, at least one working chamber
defined in said pump housing, an inlet valve controlling inlet fluid flow
into said working chamber and an outlet valve controlling outlet fluid
flow from said working chamber, a working piston mounted in said housing
to have one face defining in part said working chamber, said working
piston cyclically movable in one direction to increase the volume of said
working chamber and draw fluid into said working chamber through said
inlet valve and in the other direction to force a displaced volume of
fluid out of said working chamber through said outlet valve, drive means
driving said piston to perform said cyclical movements, a charging piston
mounted in an axial bore in said pump housing, one face defining in part
said working chamber, said charging piston movable outwardly to a
retracted end position forced against a stop by a first predetermined
minimum pressure level generated in said working chamber as said working
piston moves completely in said other direction to displace fluid from
said working chamber;
positioning means holding said charging piston in said retracted end
position against said stop as long as the pressure in said working chamber
is above a second predetermined minimum pressure substantially below said
first predetermined minimum pressure level, and means moving said charging
piston from said retracted end position towards said working piston
whenever the pressure in said working chamber declines below said second
predetermined minimium pressure level as said working piston moves in said
one direction.
2. A piston pump as claimed in claim 1 wherein the diameter of said
charging piston and of said working piston are equal, and in that said
working piston and charging piston come into contact with each other to
comprise a stop at an advanced end position of said charging piston.
3. A piston pump as claimed in claim 1, wherein said working piston and
said carrying piston are both slidably mounted in a common cylinder bore.
4. A piston pump as claimed in claim 3, wherein one of said charging piston
or said working piston includes on said face defining in part said working
chamber as extension having a peripheral surface substantially within a
wall of said cylinder bore so that the flow route to said inlet valve and
said outlet valve remains clear in all piston positions.
5. A piston pump as claimed in claim 1, wherein said means moving said
charging piston towards said working piston upon a decline in pressure in
said working chamber below said second predetermined minimum pressure
level comprises resilient means interposed between said charging piston
and said pump housing urging said charging piston away from said retracted
end position, said positioning means holding said charging piston against
the urging of said resilient means until said working chamber pressure
declines below said second predetermined minimum pressure level.
6. A piston pump as claimed in claim 5 wherein said resilient means
comprises a compression spring accommodated in an axial bore in said
charging piston.
7. A piston pump as claimed in claim 5 wherein said positioning means
includes means creating a friction force on said charging piston
sufficient so that said charging piston is held in said retracted end
position notwithstanding the urging of said resilient means by a pressure
in the working chamber of approximately 1 to 2 bar.
8. A piston pump as claimed in claim 7, wherein said charging piston is
sealed in relation to said cylinder bore by a ring seal comprising said
means creating a friction force.
9. A piston pump comprising:
a pump housing;
a bore in said pump housing defining in part a working chamber;
an inlet port in said pump housing entering into said working chamber;
an inlet valve opening upon development of a predetermined pressure
thereacross to allow fluid flow into said inlet port;
an outlet port in said pump housing entering into said working chamber;
an outlet valve opening upon development of a predetermined pressure
thereacross to allow outflow from said working chamber;
a working piston slidably mounted in said bore and having an end face
defining in part said working chamber so as to cause an increase or
decrease in the volume of said working chamber upon movement towards and
away from said working chamber;
drive means for cyclically moving said working piston in said bore towards
and away from said working chamber;
a charging piston movably mounted in said pump housing and having an end
face defining in part said working chamber; venting causing an opposite
end face to be subject to atmospheric pressure;
gripping means creating a predetermined force level of resistance to
movement of said charging piston towards said working chamber, whereby
upon movement of said charging piston towards said working chamber, the
volume of fluid drawn into said working chamber is reduced.
10. The piston pump according to claim 9, further including resilient means
creating a predetermined force urging said charging piston towards said
working chamber, said resilient force less than said force created by said
gripping means.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a piston pump, more particularly for use
in a hydraulic brake slip control apparatus, comprising a pump housing
with at least one working chamber which is connectible to supply lines via
an inlet valve and an output valve, and comprising a working piston
movable into the working chamber and drivable to perform stroke movements.
A piston pump of the mentioned type is known from German published patent
application 38 08 901. In various cases control of the flow rate supplied
to the pump is performed on the suction side. It may occur as a result
that the pressure fluid supply on the suction side is less that the
delivery rate of the pump so that cavitation in the working chamber of the
pump is encountered and, consequently, there is a risk of air being sucked
in through the piston clearance.
It is an object of the present invention to provide a piston pump of the
type referred to, the flow rate of which is dependent on the pressure
fluid supply on the suction side.
SUMMARY OF THE INVENTION
This object is achieved according to the present invention by a charging
piston which confines the working chamber and is freely movable between
two end positions defined by stops, the stroke volume of which corresponds
to the stroke volume of the working piston. The charging piston of the
piston pump according to this invention compensates for the lack of fluid
supply by its stroke movement during the suction stroke of the working
piston so that merely that quantity of pressure fluid is sucked in which
propagates via the suction valve into the working chamber. The quantity of
pressure fluid sucked in during a suction stroke of the working piston may
thus range between zero and the stroke volume of the working piston.
Cavitation in the working chamber is avoided this way. Depending on the
resistance to a change in position of the charging piston, at most a small
pressure below atmospheric pressure will occur in the working chamber,
however, without there being the risk of air intake.
When pressure below atmospheric pressure in the working chamber is to be
avoided during the suction stroke, the charging piston can be movable into
the working chamber by resilient means supported on the pump housing
according to another feature of this invention. Owing to the force of the
resilient means, the resistance to a change in position of the charging
piston can be made up for and, in addition, a suction pressure can be
determined which must prevail in the suction-side supply line in order to
permit the piston pump to receive and deliver pressure fluid.
For employing the piston pump in a brake slip control apparatus, the
charging piston is adapted to be retained in its retracted end position on
the stop of the pump housing by a pressure in the working chamber of
roughly 1 to 2 bar. In this design the pressure in the brake system can be
decreased sufficiently, and the risk of air intake after de-activation is
reliably avoided.
It can be provided in a favorable improvement of this invention that the
operating cross-sections of charging piston and working piston are of
equal size and that the working piston forms the stop for an end position
of the charging piston. This accomplishes a simple structure, and the
charging piston can be moved into its retracted end position by mechanical
contact with the working piston, the reliability being enhanced thereby.
Further, it is expedient that the charging piston is sealed in relation to
the cylinder bore by a ring seal. The resistance to a change in position
of the charging piston can be effectively increased by means of the ring
seal.
Simplification of the piston pump can be achieved further in that the
working piston and the charging piston are accommodated in one common
cylinder bore. It is suitable when the charging piston and/or the working
piston includes on its end face close to the working chamber, an
extension, the peripheral surface of which has such a distance from the
wall of the cylinder bore that the flow route to the inlet valve and to
the outlet valve remains free in all piston positions.
The resilient means according to this invention can be a compression spring
which is arranged in an axial bore in the charging piston
The present invention will be described in more detail hereinbelow by way
of an embodiment illustrated in the Figure.
DESCRIPTION OF THE DRAWING
The Figure shows a cross-section through a radial piston pump according to
the invention with a positively guided piston.
DETAILED DESCRIPTION
The illustrated radial piston pump 1 comprises a pump housing 2 with inlet
bores 3 and outlet bores 4. Inlet valves 5 are arranged in the inlet bore
3, while outlet valves 6 are arranged in the outlet bores 4. Leading from
the inlet valves 5 are inlet ports 7 and leading from the outlet valves 6
are outlet ports 8 to the working chambers 9, 10 which each are defined by
a section of a cylinder bore 11, 12, as well as by one face of an
associated working piston 15. The cylinder bores 11, 12 are arranged
radially relative to a rotatably drivable shaft 13 with an eccentric 14,
and each thereof comprises a working piston 15 which is pressed by a
spring washer 16 against a roller bearing 17 placed on the eccentric 14.
Rotation of the eccentric 14 causes the working pistons 15 to perform a
stroke movement, to cyclically increase and decrease the volume of the
working chambers 9, 10.
Radially outwardly, the working chambers 9, 10 are defined in part by
charging pistons 18 which likewise are of equal diameter with the working
piston 15 movably mounted in the cylinder bores 11, 12 to increase or
decrease the volume of the working chambers 9, 10. The charging piston 18
each also contain bores 19 accommodating compression springs 20 that
engage the end of the pump housing 2.
Projecting from each of the charging pistons 18 is a cylindrical pin
extension 21 which is of smaller diameter compared to the cylinder bore 11
and 12, respectively, the cylindrical pin extension 21 each extending into
the adjacent working chamber 9 and 10, respectively, and engage the
working pistons 15, respectively, under the action of the compression
springs 20.
The charging pistons 18 are sealed in relation to the cylinder bore 11, and
12, respectively, by a frictionally gripping ring seal 22. The radially
outward ends of the two cylinder bores 11, 12 are in communication with
the atmosphere by venting means comprising a bore 23 so that the opposite
face of the charging pistons 18 are subject to atmospheric pressure.
The resistance to a change in position of the charging pistons 18 caused by
friction and the force of the compression springs 20 are adapted to one
another such that a pressure of roughly 3 to 5 bar is necessary in the
working chambers 9, 10 in order to move the charging pistons 18 radially
outwardly into a first end position where they abut on the pump housing 2,
defining a first stop. Due to the reversal of direction during the
radially inwardly directed movement of the charging pistons 18, a pressure
of 1 to 2 bar in the working chambers 9, 10 will suffice to keep the
charging pistons 18 in their radially outward end position. The full rate
determined by the stroke volume of the working pistons 15 will hence be
attained as long as the pressure during the suction stroke of the working
pistons 15 does not fall short of the mentioned value. This happens when a
pressure of at least 3 bar prevails on the inlet bores 3 and the quantity
of pressure fluid supplied is sufficient to maintain this pressure during
the suction stroke.
Once the quantity of pressure fluid supplied to the pump becomes smaller
than the flow rate, the pressure will decrease on opening of the inlet
valves 5 below the pressure required to maintain the position of the
charging pistons 18 . The charging pistons 18 will then be moved by the
compression springs 20 towards the working pistons 15 to decrease the
volume of the working chambers 9, 10 as a result, to thereby compensate
for the insufficient pressure fluid supply.
If a partial quantity of pressure fluid was still delivered during the
suction phase, the charging pistons 18 will be kept spaced from the
working pistons by way of the pressure-fluid cushion prevailing in the
working chambers 9, 10 after the inlet valves 5 are closed and, during the
subsequent pressure stroke, are urged by this cushion to return to their
radially outward end position. As soon as the charging pistons 18 abut on
the pump housing 2, the pressure can rise further in the working chambers
9, 10, and the partial quantity sucked in can displace through the outlet
valves 6.
When the pressure fluid supply on the inlet bores 3 ceases, the charging
pistons 18 will move pin extensions 21 into abutment with the working
pistons 15, comprising a second stop, setting a second end position of the
charging piston 18 and, due to the mechanical contact, are moved to and
fro together with the working pistons 15. A pressure fluid cushion is
maintained in the working chambers 9, 10 hereby, so that cavitation and
the sucking in of air are not allowed to occur. The maximum displaced
volume of the working piston 15 and that of the charging piston 18 are
equal to produce this result.
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